This invention relates to a coating process for applying a coating liquid to a substrate such as a glass substrate for a liquid crystal display (LCD), thereby forming a coating film such as a photoresist coating or an anti-reflective coating.
The LCD manufacturing process employs photolithography as the manufacturing process of a semiconductor device. In the photolithography for the LCD, a resist coating is formed on a glass substrate, and subjected to pattern exposure and then development. A semiconductor layer, an insulating layer and an electrode layer formed on the substrate are selectively etched, thereby forming an ITO (Indium Tin Oxide) thin film or electrode pattern, etc.
To coat the LCD substrate with a resist liquid, so-called spin coating is used. The spin coating is performed using a coating apparatus as disclosed in U.S. Pat. No. 5,688,322. In this coating apparatus, an LCD substrate is held by a spin chuck, a solvent and a resist liquid are dripped onto the substrate, and the spin chuck and a rotary cup are rotated in synchronism with each other, with the upper opening of the cup closed with a lid. Liquid drips or mist scattering from the substrate are received by a drain cup, thereby exhausting liquid components in the form of, for example, droplets to the outside of the cup through a plurality of liquid exhaust pipes, and gaseous components in the form of, for example, mist to the outside of the cup through a plurality of gas exhaust pipes.
Since each gas exhaust pipe opens to the periphery of the drain cup, that part of the mist which exists in the vicinity of the openings (exhaust ports.) of the exhaust pipes is first exhausted, and thereafter the exhaust area gradually increases within the cup. Therefore, it is difficult to promptly exhaust the entire internal area of the cup.
The size of LCD substrates has recently increased from (650xc3x97550 mm) to (830xc3x97650 mm). If the substrate size more and more increases in near future, coating the substrate with a resist liquid will cause generation of a great amount of mist which may contaminate the resist coating. Since in particular, it is difficult to perform complete exhaustion after the rotation of the substrate is stopped, the resist coating is more likely to be contaminated by the mist. A great amount of mist is hard to sufficiently separate into a gas and a liquid in the drain cup, and hence a gas/liquid mixture will be exhausted through the gas exhaust pipes. This means that a great amount of mist will enter the gas exhaust pipes.
It is the object of the invention to provide a coating process which are free from contamination of a coating on a substrate by mist of a coating liquid.
The inventors have found that if the amount of exhaustion within the cup is simply increased, the influence of gas flow due to exhaustion will increase, which makes it difficult to form a uniform resist coating on an LCD substrate, and which increases the range of variations in the thickness of the resist coating, particularly in the case of a large LCD substrate. In light of this, the inventors have developed an invention as described below, as a result of deep and serious research.
According to an aspect of the invention, there is provided a process of forming a coating on a substrate within a cup section which has an upper opening and an exhaust port, comprising the steps of: (a) carrying a substrate into the cup section through the upper opening, and holding the substrate by a spin chuck; (b) applying a coating liquid to the substrate while exhausting the cup section through the exhaust port; (c) rotating the spin chuck and the substrate while exhausting the cup section through the exhaust port, thereby diffusing the coating liquid applied to the substrate in the step (b) to form a coating on the substrate; (d) stopping the rotation of the substrate and carrying the substrate with the coating out of the cup section; and (e) changing, during the step (c) or (d), the amount of exhaustion of the cup section to a value greater than a greater one of the amounts of exhaustion assumed in the steps (b) and (c), in order to exhaust, from the cup section, a mist of the coating liquid which occurs during the step (c).
The cup section includes an inner cup which surrounds the substrate, and an outer cup which surrounds the inner cup, communicates with the inner cup and the exhaust port, and has a gas/liquid separating member; and in the step (e), an excreta which contains a mist of the coating liquid exhausted from the inner cup is separated into a liquid component and a gas component by the gas/liquid separating member, and the mist of the coating liquid is exhausted through the exhaust port.
It is preferable that in the step (c), the lid is mounted on the cup section to close the upper opening, and the substrate is raised to approach the lid such that it is opposed to the lid at a level higher than the exhaust port.
It is also preferable that in the step (e) to raise the substrate while the lid is raised. In this case, it is preferable that the raising speed of the substrate is higher than the raising speed of the lid.
Further preferably, in the steps (b), (c) and (e), exhaustion of the cup section is performed through the exhaust port in a direction opposite to the direction of rotation of the substrate, and in a circumferential direction.
According to another aspect of the invention, there is provided a process of forming a coating on a substrate within a cup section which has an upper opening and an exhaust port, comprising the steps of: (a) carrying a substrate into the cup section through the upper opening, and holding the substrate by a spin chuck; (b) applying a coating liquid to the substrate while exhausting the cup section through the exhaust port; (c) rotating the spin chuck and the substrate while exhausting the cup section through the exhaust port, thereby diffusing the coating liquid applied to the substrate in the step (b) to form a coating on the substrate; (d) stopping the rotation of the substrate and carrying the substrate with the coating out of the cup section; and (h) raising the substrate to a level higher than the exhaust port while rotating the substrate in the step (c).
In the step (h), it is preferable that the substrate is raised while the lid is raised. In this case, it is also preferable that the raising speed of the substrate is higher than the raising speed of the lid. It is further preferable that the substrate is made to approach the lid to define therebetween a narrow clearance. In addition, it is desirable that during the step (c) or (d), the amount of exhaustion of the cup section should be changed to a value greater than a greater one of the amounts of exhaustion assumed in the steps (b) and (c), in order to exhaust, from the cup section, a mist of the coating liquid which occurs during the step (c).
Furthermore, a mist of the coating liquid may be introduced through the exhaust port into an exhaustion passage in a direction opposite to the direction of rotation of the substrate. In this case, it is desirable that a plurality of exhaust ports should be arranged symmetrical with respect to the center of rotation of the substrate, and that the diameter of each exhaust port viewed along the axis of the outer cup should be smaller than the diameter thereof viewed along the circumference of the outer cup.
Since in the invention, the exhaust port is connected to the gas exhaust pipe such that the direction of flow of a fluid (mist) from the exhaust port to the exhaust pipe is opposite to the direction of rotation of the substrate, it is hard for mist to directly enter the gas exhaust pipe. In addition, since in the invention, the gas exhaust pipe is connected to a lower portion of the outer peripheral wall of the outer cup to thereby define a zigzag passage together with the gas/liquid separating member, mist is prevented from directly entering the gas exhaust pipe, thereby further promoting gas/liquid separation of the mist.
Also, since the gas exhaust port is constructed such that a diameter thereof when viewed in a radial direction of the outer cup is greater than a diameter thereof when viewed in an axial direction of the outer cup, the open area of each gas exhaust port with respect to the outer cup (drain cup) is large, and hence exhaustion of mist from the outer cup can be performed smoothly. As a result, the atmosphere around the substrate can be promptly cleaned.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.